*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #0d0d0d;
  --panel: #141414;
  --border: #2a2a2a;
  --num-bg: #1c1c1c;
  --num-hover: #272727;
  --op-bg: #1a1a2e;
  --op-hover: #22224a;
  --op-color: #7b7fff;
  --eq-bg: #e8ff00;
  --eq-hover: #f5ff55;
  --eq-color: #0d0d0d;
  --fn-bg: #1e1e1e;
  --fn-hover: #2c2c2c;
  --fn-color: #aaa;
  --text: #f0f0f0;
  --dim: #555;
  --font-mono: 'Share Tech Mono', monospace;
  --font-display: 'Bebas Neue', sans-serif;
  --radius: 6px;
  --gap: 10px;
}

body {
  background: var(--bg);
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
  background-image:
    radial-gradient(ellipse at 20% 50%, rgba(123,127,255,0.06) 0%, transparent 60%),
    radial-gradient(ellipse at 80% 20%, rgba(232,255,0,0.04) 0%, transparent 50%);
}

.calculator {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 24px;
  width: 320px;
  box-shadow:
    0 0 0 1px #000,
    0 30px 80px rgba(0,0,0,0.7),
    inset 0 1px 0 rgba(255,255,255,0.04);
  position: relative;
}

.brand {
  font-family: var(--font-display);
  font-size: 13px;
  letter-spacing: 4px;
  color: var(--dim);
  text-align: center;
  margin-bottom: 20px;
}

.display {
  background: #0a0a0a;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px 18px 12px;
  margin-bottom: 18px;
  min-height: 90px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  overflow: hidden;
}

.expression {
  font-size: 13px;
  color: var(--dim);
  min-height: 20px;
  word-break: break-all;
  text-align: right;
  transition: opacity 0.15s;
}

.result {
  font-family: var(--font-display);
  font-size: 48px;
  color: var(--text);
  letter-spacing: 2px;
  line-height: 1;
  margin-top: 4px;
  transition: transform 0.1s ease, color 0.2s;
  word-break: break-all;
  max-width: 100%;
}

.result.pop {
  transform: scale(1.04);
  color: var(--eq-bg);
}

.buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--gap);
}

.btn {
  background: var(--num-bg);
  border: 1px solid transparent;
  border-radius: var(--radius);
  color: var(--text);
  font-family: var(--font-mono);
  font-size: 18px;
  height: 60px;
  cursor: pointer;
  transition: background 0.12s, transform 0.08s, border-color 0.12s;
  display: flex;
  align-items: center;
  justify-content: center;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.btn:hover { background: var(--num-hover); border-color: var(--border); }
.btn:active { transform: scale(0.93); }

.btn.fn { background: var(--fn-bg); color: var(--fn-color); }
.btn.fn:hover { background: var(--fn-hover); }

.btn.op { background: var(--op-bg); color: var(--op-color); font-size: 20px; }
.btn.op:hover { background: var(--op-hover); border-color: var(--op-color); }
.btn.op.active { background: var(--op-color); color: #fff; }

.btn.eq {
  background: var(--eq-bg);
  color: var(--eq-color);
  font-size: 22px;
  font-weight: bold;
  border-color: transparent;
}
.btn.eq:hover { background: var(--eq-hover); }

.span-two { grid-column: span 2; }

/* Ripple */
.btn { position: relative; overflow: hidden; }
.ripple {
  position: absolute;
  border-radius: 50%;
  background: rgba(255,255,255,0.12);
  transform: scale(0);
  animation: ripple-anim 0.45s linear;
  pointer-events: none;
}
@keyframes ripple-anim {
  to { transform: scale(4); opacity: 0; }
}

@media (max-width: 360px) {
  .calculator { width: 290px; padding: 18px; }
  .result { font-size: 40px; }
}